In their interior, HPT blades have available a relatively complex system of channels for air cooling. For manufacturing such HPT blades with such a system of channels, they are cast, for example, whereby during the casting, an expensive core system is employed to form the system of channels.
Owing not least to this expensive manufacturing process, such high pressure turbine blades are very expensive, so that a single blade can evoke costs running to a five-figure amount in euros.
With this as the background, it is desirable to repair damaged high pressure turbine blades, in fact it is more cost-effective than would correspond to production of a new part.
An exemplary procedure for repair of a turbine blade is disclosed in U.S. 2005/0091848 A1. Also, DE 10 2005 002 609.5 by the applicant discloses a procedure for repair of turbine blades.
The problems presented in repair of high pressure turbine blades are considerably greater than with compressor blades. This is to be traced back not least to the discussed expensive system of channels within the high pressure turbine blade, which system of channels is lacking in compressor blades. Damage to high pressure turbine blades that appear beneath the tip area, have, so far as is known to the applicant, is in fact repairable with moderate success, with limitations existing especially regarding the overall crack length and crack position. When a replacement part is fitted in, for example via diffusion bonding or diffusion soldering, or via beam welding (LB welding or EB welding), the problem is to fit a replacement part manufactured by welding to the existing contour of the remainder of the blade sheet. However, it can deviate substantially from the desired contour.